Valve seat inserts

ABSTRACT

A VALVE SEAT INSERT HAVING IMPROVED MECHANICAL PROPERTIES AND BEING SUBSTANTIALLY NICKEL FREE, THE INSERT HAVING A COMPOSITION CONTAINING FROM 1.00 TO 2.25% CARBON, A MAXIMUM OF 0.75%MANGANESE, A MAXIMUM OF   1.00% SILICON, FROM 28 TO 32% CHROMIUM, FROM 18 TO 30% COBALT, FROM 2 TO 8% TUNGSTEN, WITH THE BALANCE SUBSTANTIALLY IRON EXCEPT FOR INCIDENTAL IMPURITIES.

Oct. 31, 1972 D. o. sTANLE 3,701,652

VALVE SEAT INSERTS Filed Jan. 19, 1971 ,3 5 2O 2 III F a: 2 g: :5-

5 I I l J I l l i 0 COBALT ,INVENTORV De/mar 0 sfaa/ey I I Q522 Q@WATTORNEYS U-S. Cl. 75-126 A 5 Claims ABSTRACT OF THE DISCLOSURE UnitedStates Patent A Valve seat insert having improved mechanical propertiesand being substantially nickel free, the insert having a compositioncontaining from 1.00 to 2.25% carbon, a maximum of 0.75% manganese, amaximum of 1.00% silicon, from 28 to 32% chromium, from 18 to 30%cobalt, from 2 to 8% tungsten, with the balance substantially ironexcept for incidental impurities.

BACKGROUND OF THE INVENTION Field of the invention This invention is inthe field of valve seat inserts which are received in the engine .blockfor seating an exhaust valve, the insert being composed of an iron basealloy containing substantially no nickel but having hardness,compressive yield strength and creep resistance equivalent to or greaterthan the more expensive nickel base alloys.

DESCRIPTION OF THE PRIOR ART A valve seat insert ring by its naturepresents stringent requirements insofar as physical and mechanicalproperties are concerned. Since modern day engines operate atsubstantially elevated temperatures they must have high temperatureproperties in combination which are not ordinarily found in inexpensivealloys.

A description of the problems of securing adequate mechanical propertiesin valve seat inserts will be found in Armstrong US. Pat. No. 2,768,918and Prasse et al. US. Pat. No. 2,805,943, both owned by the assignee ofthe present application. 'In the Armstrong patent, there is adescription of an iron base valve seat insert containing substantialamounts of silicon (1.9 to 2.6%) and nickel (1.0 to 1.6%). The Prasse etal. patent describes a cast valve seat insert consisting of an iron basematerial containingfrom 27 to 33% chromium and 10 to 14% cobalt. Whileeach of these valve seat inserts has improved mechanical properties athigh temperatures, they do not retain all these properties when anoperating temperature of 1,000 F. and higher is reached.

Presently, most of the valve seat insert rings used in high temperature,heavy duty engines have substantial amounts of nickel. However, thecurrent shortage of nickel and its high cost are distinct drawbacks tothe continued use of these alloys.

It was found that conventional martensitic grades of iron base alloysare not appropriate for this use because of their inherent low creepresistance at operating temperatures of 1,000 F. It was also found thatconventional austenitic stainless steels would not be satisfactorybecause of their low hot hardness at 1,000 E, as compared to nickel basealloys. Cobalt base alloys are too expensive for this type ofapplication.

SUMMARY OF THE INVENTION The present invention provides a valve seatinsert ring which combines the better properties of austenitic "icestainless steels with cobalt based hard facing materials and provides acobalt containing stainless steel hardened by chromium and tungstencarbides. While the alloy materials used for the purpose of the presentinvention are nickel free (except as nickel may occur as an impurity inthe iron) their mechanical properties at elevated temperatures arecertainly comparable to and in some cases exceed the mechanicalproperties of the nickel alloys which are presently being used. Theseimprovements in properties are accompanied by a significant reduction incost. 7

The valve seat insert rings of the present invention have a compositionincluding 1.00 to 2.25% carbon, a maximum of 0.75% manganese, a maximumof 1.00% silicon, from 28 to 32% chromium, from 18 to 30% cobalt, from 2to 8% tungsten, with iron being substantially the balance. It has beenfound that the amount of cobalt present is particularly critical toachieve the improved results. At cobalt concentrations of less than 18%,the amount of martensite in the microstructure of the insert issubstantially increased. However, at cobalt contents of 18% and above,the percentage of martensite in the as-cast alloy is reduced to a valuebelow 10%. The reduction of the amount of martensite present has beenfound to substantially improve the creep relaxation properties of thevalve seat insert.

BRIEF DESCRIPTION OF THE DRAWINGS Other objects, features and advantagesof the invention will be readily apparent from the following descriptionof certain preferred embodiments thereof, taken in conjunction with theaccompanying drawings, although variations and modifications may beeffected without departing from the spirit and scope of the novelconcepts of the disclosure, and in which:

FIG. 1 is a fragmentary cross-sectional view, partly in elevation, ofthe valve port area of an internal combustion engine employing a valveseat insert of the present invention;

FIG. 2 is a plan view of the valve seat insert on an enlarged scale; and

FIG. 3 is a graph plotting the percentage of martensite in the insertring structure as a function of the amoun of cobalt present. 9

DESCRIPTION OF THE PREFERRED EMBODIMENTS In FIG. 1, reference numeral 10indicates generally an engine block composed of cast iron or the likeand having a discharge port 11 in which a poppet-type exhaust valve 12is arranged to reciprocate and thereby discharge hot combustion gases tothe exhaust system. At the exhaust opening, there is provided a valveseat insert ring 13 which is press fitted in an annular recess 14 formedin the engine block 10. A valve stem guide 15 is press fitted in a bore16 concentric with the recess 14. The valve seat insert ring 13 has acylindrical outer peripheral wall 13a, a fiat bottom 13b, a flat top 13cand a tapered seating face 13d converging from the fiat top to acylindrical inner peripheral wall 13a. The valve seat insert ring 13 isthus under substantial compression during operation of the engine and isfurther subjected to substantial pounding by the seating of the poppetvalve 12 after the exhaust cycle of the engine.

Considerable experimentation has resulted in the development of a valveseat insert ring which can retain its hard hardness properties atelevated temperatures above 1,000 C., and which resists compressivecreep and yielding at those elevated temperatures. The broad range ofthe improved alloy composition used for the insert ring is as follows:

Carbon 1.00 to 2.50% by weight. Manganese 0.75% maximum. Silicon 1.00%maximum. Chromium 28 to 32%.

Cobalt 18 to 30%.

Tungsten 2 to 8%.

Iron Substantially the balance.

Within the broader ranges set forth above, a particularly preferredalloy composition is the following:

Carbon 1.70 to 2.25%

Manganese 0.75% maximum.

Silicon 7 1.00% maximum. Chromium 28 to 32%.

Cobalt 20 to 24%.

Tungsten 6 to 8%.

Iron Substantially the balance.

The best overall balance of properties exists in an insert ring having anominal composition including about 2% carbon, about 1% silicon, about30% chromium, about 20% cobalt, about 7% tungsten, and the balancesubstantially. iron.

A series of alloys falling within the compositional ranges set forthabove were compared in physical properties to those possessed by thestandard nickel base alloy (VMS 434) which has a nominal analysiscontaining 2.50% carbon, 20% chromium, 40% nickel, 12% cobalt, 6%tungsten, a maximum of 1% silicon, and the balance substantiallyiron-This nickel base alloy is referred to as the control in succeedingportions of this specification.

Four alloys were made up having the following norminal analyses:

Alloy C Si Cr W Go Fe 14 0. 91 31. 54 7. 33 20. 23 39. 30 1. 31. 80 7.12 29. 92 29. 40 0. s7 30. 95 7. 4s 20. 71 40. 0 0. s1 29. 72 7. 28 21.19 40. 16

The following hardness and compressive yield-strengths were obtained onthe alloys at various temperatures:

. Room Compressive temp. BHN BHN yield strength Alloy Rs 1,000 F. 1,200F. at 1,000 F.

Control 35 289 225 82, 000

The compressive creep strength at 1,000 F. for the new alloys of thepresent invention compared very favorably with that of the control. Theresults are summarized in the Oxidation tests were run on alloy I 12 at1600 F. for 120 hours. The alloy had a weight gain of only 0.0112 gramper square decimeter, an exceptionally low value.

The physical and mechanical properties achieved in the new materials isdone at a substantial saving in cost. For example, the raw materialsgoing into alloy I 12 cost about 42% less than those in the control.

The amount of martensite appears to have a definite bearing upon theretention of high temperature properties in these alloys. As evidentfrom the curve of FIG. 3, where actual experimental results areplotte-d,there is a discontinuity in the curve at a cobalt content ofapproximately 18%. It will be seen that at a 10% cobalt concentration,the alloy contains about 27% martensite, whereas at cobalt contents of18% and greater, less than 10% martensite is present.

From the foregoing, it will be understood that the valve seat inserts ofthe present invention provide completely satisfactory mechanicalproperties at elevated temperatures While achieving a substantialreduction in cost.

I claim as my invention:

1. A valve seat insert for an internal combustion engine comprising aring having a valve seating face thereon, said ring having the followingcomposition:

Carbon 1.00 10 2.50% by weight.

Manganese 0.75% maximum. Silicon -2 1.00% maximum. Chromium 28 tof32%.Cobalt 18 to 30%.

Tungsten 2 to 8%.

Iron Essentially the balance.

2. The valve seat insert of claim 1 in which the ring has the followingcomposition:

Carbon 1.70 to 2.25%. Manganese 0.75% maximum. Silicon 100% maximum.Chromium 28 to 32%.

Cobalt 20 to 24%.

Tungsten 6 t0 8%. Iron Essentially the balance.

3. The valve seat insert of claim 1 in which the microstructure of saidring contains no more than about 10% martensite.

4. The valve seat insert of claim 1 which contains about 2% carbon,about 1% silicon, about 30% chromium, about 20% cobalt, about 7%tungsten, and the balance essentially iron.

5. The valve seat insert of claim 6 in the as cast con- CHARLES N.LOVELL, Primary Examiner Us. 01. X.R. -122, 126 c, 126 H, 126 R; 123-188AA; 148.-'-31

1.00% SILICON, FROM 28 TO 32% CHROMIUM, FROM 18 TO 30% COBALT, FROM 2 TO8% TUNGSTEN, WITH THE BALANCE SUBSTANTIALLY IRON EXCEPT FOR INCIDENTALIMPURITIES.